This invention relates generally to xerographic copying apparatus and, more particularly, to a contact fusing system for fixing electroscopic toner material to a support member.
In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual image can be either fixed directly upon the photosensitive member or transferred from the member to a sheet of plain paper with subsequent affixing of the image thereto.
In order to permanently affix or fuse electroscopic toner material onto a support member by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This action causes the toner to be absorbed to some extent into the fibers of the support member which, in many instances, constitutes plain paper. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be firmly bonded to the support member. In both the xerographic as well as the electrographic recording arts, the use of thermal energy for fixing toner images onto a support member is old and well known.
One approach to thermal fusing of electroscopic toner images onto a support has been to pass the support with the toner images thereon between a pair of opposed roller members, at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the fuser roll to thereby effect heating of the toner images within the nip. By controlling the heat transferred to the toner, virtually no offset of the toner particles from the copy sheet to the fuser roll is experienced under normal conditions. This is because the heat applied to the surface of the roller is insufficient to raise the temperature of the surface of the roller above the "hot offset" temperature of the toner whereat the toner particles in the image areas of the toner would liquify and cause a splitting action in the molten toner to thereby result in "hot offset". Splitting occurs when the cohesive forces holding the viscous toner mass together is less than the adhesive forces tending to offset it to a contacting surface such as a fuser roll.
Occasionally, however, toner particles will be offset to the fuser roll by an insufficient application of heat to the surface thereof (i.e. "Cold" offsetting); by imperfections in the properties of the surface of the roll; or by the toner particles insufficiently adhering to the copy sheet by the electrostatic forces which normally hold them there. In such a case, toner particles may be transferred to the surface of the fuser roll with subsequent transfer to the backup roll during periods of time when no copy paper is in the nip.
Moreover, toner particles can be picked up by the fuser and/or backup roll during fusing of duplex copies or simply from the surroundings of the reproducing apparatus.
One arrangement for minimizing the foregoing problems, particularly that which is commonly referred to as "offsetting" has been to provide a fuser roll with an outer surface or covering of polytetrafluoroethylene, commonly known as Teflon, to which a release agent such as silicone oil is applied, the thickness of the Teflon being on the order of several mils and the thickness of the oil being less than 1 micron. Silicone based oils, which possess a relatively low surface energy, have been found to be materials that are suitable for use in the heated fuser roll environment where Teflon constitutes the outer surface of the fuser roll. In practice, a thin layer of silicone oil is applied to the surface of the heated roll to thereby form an interface between the roll surface and the toner images carried on the support material. Thus a low surface energy layer is presented to the toner as it passes through the fuser nip and thereby prevents toner from offsetting to the fuser roll surface. The silicone oil or other suitable release agent is conventionally applied to the fuser roll structure by wick or other suitable means which serves to remove those toner particles whice do find their way onto the fuser roll.
It is also desirable to provide a cleaning structure for the backup roll for removing toner therefrom, particularly, when the fuser is utilized in a duplex mode of operation. In certain prior art fusing devices, the backup roll is provided with a Teflon sleeve which is cleaned by contact with a web, wick or brush without the aid of oil or other release agent being applied thereto. It has been observed that continued operation at elevated temperatures such as exhibited in the fusing environment of a xerographic reproducing apparatus, the life expectancy of material such as Teflon is somewaht curtailed.
Silicone rubbers and other temperature resistant elastomeric materials such as Viton employed for backup roll constructions have been found to better withstand such operating conditions. Viton is a trademark of E. I. duPont de Nemours and Co. which covers a series of fluoroelastomers based on the copolymer of vinylidene fluoride and hexafluoropropylene. However, they do not readily lend themselves to being cleaned by the aforementioned techniques. This is due to a large extent to the relatively high coefficient of friction and asperities in the surface of the elastomeric surface.
Accordingly, it is the principal object of this invention to provide a new and improved copier apparatus.
It is a more particular object of this invention to provide a new and improved contact fuser for fixing toner images to support sheets.
Another object of this invention is to provide a new and improved cleaning system and method of fabrication thereof which cleaning system is utilized in conjunction with an elastomeric fuser member of a system for fixing toner images to support sheets.